1. Field of the Invention
This invention relates to the field of mattress and cushion pads primarily intended for hospital use to reduce the development of decubitus ulcers in patients using the pads.
2. Discussion of the Background
Decubitus ulcers, commonly referred to as bed or pressure sores, are a major health concern for patients that become bed or chair bound for prolonged periods of time. They are also frequent complications for burn victims and tall, thin patients and other patients with particularly bony protuberances. The ulcers generally develop at such bony protuberances as well as other relatively bony areas of the patient's body including the trochanteric (hip) area, scapula (shoulder blade) area, spinal area, and coccyx (tailbone) area where relatively little flesh is present and blood circulation is often poor.
Factors contributing to the development of the decubitus ulcers are numerous including the general overall condition of the patient's skin and underlying tissue; however, forces generated on the patient's body by the mattress pad or other support are also critical. These forces include both normal and lateral or shearing forces. Reduction of such forces has been attempted and accomplished in a variety of product designs with varying degrees of success and widely varying costs. Such product designs extend the gambit from, for example, standard hospital mattresses on one end to more exotic and expensive designs such as fluidized, specialty beds on the other.
Standard hospital mattresses and cushions are generally not considered as anti-decubitus products and, in fact, are often the primary cause of the decubitus ulcers in the patients using them. While certainly providing a degree of comfort over a limited time, conventional hospital mattresses commonly create pressure points and localized areas of relatively high, normal forces on the patient's body that may result directly in decubitus ulcers. Such normal pressures and forces when excessive or prolonged can cause localized occlusion of capillary blood flow depriving the skin and underlying tissue of needed oxygen and nutrition. Conventional mattresses can also offer significant resistance to lateral movement of the patient as he or she rolls over or otherwise moves or is moved across or along the mattress. Such resistance can create substantial lateral shear forces which may also cause occlusion of the capillary blood flow as well as cause direct structural failure or rupture of the skin and underlying tissue.
To improve the anti-decubitus properties of standard hospital mattresses, overlays are often used as a first measure. Such overlays, for example, may include convoluted foam pads of various thicknesses and densities which are quite common and inexpensive. The foam overlays generally are relatively thin and do a marginal job of reducing pressure points and high normal forces but have no mechanism for reducing lateral shear forces. Inflatable overlays are also widely used to reduce normal forces but like foam ones, they are relatively thin and have no mechanism for reducing shear forces. They are also prone to puncture failure and leakage and like most overlays, are usually difficult to clean and sanitize. Consequently, they are for the most part not reusable from one patient to the next. Inflatable overlays typically consist of a sealed vinyl bladder that is inflated manually or by an air pump. The more sophisticated and expensive models have a plurality of air chambers within the sealed bladder wherein adjacent chambers are alternately inflated and deflated (e.g., every 5-10 minutes). This serves to vary the support to areas of the patient's body to prevent any long term development of pressure points and the accompanying occlusion of blood flow that can lead to the development of the decubitus ulcers. However, in addition to the potential failure by puncture or leakage, the performance of such inflatable overlays depends greatly upon proper initial and continuing operation particularly in regard to correct inflation with respect to each patient's size, weight, and position.
Devices that are designed to replace the conventional hospital mattress altogether but still use the existing hospital bed frame are commonly referred to as "mattress replacements." Such replacements are normally categorized into two groups (i.e., dynamic and static or passive). Dynamic ones as the name implies are operationally active and require an external power source. In a large number of them, they employ pneumatic technology including some basic concepts used in inflatable overlays as discussed above (e.g., alternating inflating/deflating of adjacent air chambers). However, because of the use of external power sources, such pneumatic mattress replacements can also employ more advanced and complicated features such as isolating individual air chambers or zones and selectively controlling and adjusting the pressure in them. In this manner, pressure can be reduced, for example, in those chambers or zones where the risk of tissue breakdown is relatively high while pressure can be increased in the remaining chambers or zones where the risk of sore development is relatively low. Still other pneumatic mattress replacements maintain and monitor air flow through the bladder to control moisture and temperature at the interface of the patient's body on the mattress. This is usually done in systems classified as low air loss ones meaning that there is a predetermined amount of "air loss" or air flow through the inflated mattress. The air flow is then monitored and controlled for the desired moisture content and temperature. Dynamic mattress replacements often retail in the range of $2,000-$6,000 and are commonly leased or rented to the user or hospital because of the maintenance and repair requirements inherent in any such active systems.
Static or passive mattress replacements require no external power to operate and rely on a combination of materials and mechanical elements to achieve reduced normal or interface pressure between the patient's body and the mattress. The performance of static mattress replacements is generally not as high as the dynamic ones; however, they are very popular due to their reliability, maintainability, and relatively low cost ($500-$1,000). They are also for the most part very user friendly in the sense that there is very little if any need for the user to monitor or adjust any controls or other settings. Examples of static or passive systems would be simple waterbeds as well as designs that employ specially configured foam components or bladders filled with gels, air, or other fluids. In addition to their relatively low cost, the primary desirability of static or passive mattress replacements over the dynamic ones is that they do not have any externally powered components (with their inherent degree of additional complexity, cost, and maintenance).
Still other products that are designed to reduce the development of decubitus ulcers include specialty beds. Such specialty beds are typically integrated with their own bed frame and control systems that allow the user to adjust or control a variety of features. There are several types of such specialty beds including low air loss beds, fluidized bead beds, and spinal cord injury beds. The low air loss beds include many of the features of low air loss, replacement mattresses discussed above but generally on a more sophisticated level. Like the mattress replacement, low air loss, specialty beds commonly include a series of inflatable, adjacent chambers or zones which can be selectively inflated or deflated to obtain the desired support. Additionally, the control systems on such low air loss, specialty beds may regulate the air pressure to each individual chamber or zone of chambers. They may also monitor and control the moisture and temperature of the air that circulates through the air chambers or zones. In one common mode of operation, moisture from the patient's body is wicked away from the patient through the surface material of the bed into the chambers or zones where it is then evaporated and subsequently removed or exhausted by the circulation of fresh air through the system. Some low air loss, specialty beds also employ the alternating support concept discussed above with the more sophisticated ones even allowing the specific placement of shaped or profiled pillows which enable positioning and immobilization of the patient as desired. Still others include a turning feature which rotates the entire support surface and patient about the longitudinal axis of the bed. Understandably, the degree of complexity of these specialty beds inherently demands extensive maintenance and service requirements. Nevertheless, the overall performance is good and many victims of pressure sores or decubitus ulcers are placed on these types of beds for cure. Unfortunately, the high initial cost of these specialty beds (e.g., $10,000 to $40,000) as well as the high rental or lease rate (e.g., $80-$125 per day) limit their wide usage.
Of the specialty beds, perhaps the most effective are the fluidized bead beds. Such beds are considerably different from most other support systems in that the patient is supported by approximately 1200-1500 pounds of silica beads which are fluidized by a continuous flow of air from underneath the patient. A filter sheet separates the patient from the beads but allows the flow of air to pass through. This type of surface provides excellent pressure relief (i.e., virtually no normal pressure points) and also offers significantly reduced resistance (i.e., very low lateral or shearing force) to the patient's body as he or she moves or is moved across or along the bed. Nevertheless, fluidized bead beds do have several distinct disadvantages in addition to cost and complexity including the fact that they must remain in a horizontal position and they can cause severe dehydration in the patient due to the constant air flow past the patient's body. Also, patient transfers to and from the bed are often complicated due to the tub-like structure that contains the fluidized beads. Further, the entire volume of the beads must be cleaned and reprocessed after each patient's use.
With the above in mind, the anti-decubitus mattress pad of the present invention was developed. With it, the reduction of both normal and lateral forces and pressures on the patient's body such as currently achieved for the most part only in the higher priced and more complex specialty beds can now be offered in a less expensive, static, reusable mattress replacement design.